Melt-processible poly(tetrafluoroethylene)

ABSTRACT

Melt-processible, thermoplastic poly(tetrafluoroethylene) (PTFE) compositions are disclosed and methods for making and processing same. Additionally, products comprising these compositions are described.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Divisional of U.S. application Ser. No. 09/369,319 filed Aug.6, 1999 allowed. Furthermore, this application claims the benefit ofU.S. provisional application No. 60/095,583 filed Aug. 6, 1998 theentire disclosure of which is hereby incorporated reference.

FIELD OF THE INVENTION

This invention relates to melt-processible poly(tetrafluoroethylene)(PTFE), compositions thereof, articles formed therefrom, and methods formaking the same. More particularly, the present inventions relates to aparticular range of poly(tetrafluoroethylene) polymers which are readilymelt-processible while maintaining good/suitable mechanical properties.Further, the present invention relates to products made ofmelt-processible, thermoplastic PTFE compositions.

BACKGROUND OF THE INVENTION

Poly(tetrafluoroethylene) (PTFE) is well-known for, among otherproperties, its chemical resistance, high temperature stability,resistance against ultra-violet radiation, low friction coefficient andlow dielectric constant. As a result, it has found numerous applicationsin harsh physico-chemical environments and other demanding conditions.Equally well-known is the intractability of this important polymer.Numerous textbooks, research articles, product brochures and patentsstate that PTFE is intractable because, above its crystalline meltingtemperature, it does not form a fluid phase that is of a viscosity thatpermits standard melt-processing techniques commonly used for mostthermoplastic polymers (Modern Fluoropolymers, J. Scheirs, Ed. Wiley(New York), 1997; The Encyclopaedia of Advanced Materials, Vol. 2, D.Bloor et al. Eds., Pergamon (Oxford) 1994; WO 94/02547; WO 97/43102).Suitability of a polymer for standard melt-processing techniques may beevaluated, for example, through measurement of the melt-flow index ofthe material (cf. ASTM D1238-88). Melt-processible polymers should,according to this widely employed method, exhibit at least a non-zerovalue of the melt-flow index, which is not the case for common PTFEunder testing conditions that are representative of, and comparable tothose encountered in standard polymer melt-processing. The extremelyhigh viscosity of PTFE, reported to be in the range of 10¹⁰-10¹³ Pa.s at380° C., is believed to be associated, among other things, with anultra-high molecular weight of the polymer, which has been estimated tobe in the regime well above 1,000,000 g/mol and often is quoted to be ofthe order of 10,000,000 g/mol. In fact, it is claimed (ModernFluoropolymers, J. Scheirs, Ed. Wiley (New York), 1997, p. 240) that “toachieve mechanical strength and toughness, the molecular weight of PTFEis required to be in the range 10⁷-10⁸ g/mol . . . ” Due to this highviscosity, common PTFE is processed into useful shapes and objects withtechniques that are dissimilar to standard melt-processing methods.Rods, sheets, membranes, fibers and coatings of PTFE are produced by,for example, ram-extrusion, pre-forming and sintering of compressedpowder, optionally followed by machining or skiving, paste-extrusion,high isostatic pressure processing, suspension spinning, and the like,and direct plasma polymerization. Unfortunately, these methods generallyare less economical than common melt-processing, and, in addition,severely limit the types and characteristics of objects and productsthat can be manufactured with this unique polymer. For example, commonthermoplastic polymers, such as polyethylene, isotactic polypropylene,nylons, poly(methylmethacrylate) polyesters, and the like, can readilybe melt-processed into a variety forms and products that are of complexshapes, and/or exhibit, for example, some of the followingcharacteristics: dense, void-free, thin, clear or translucent; i.e.properties that are not readily, if at all, associated with productsfabricated from PTFE.

The above drawback of PTFE has been recognised virtually since itsinvention, and ever since, methods have been developed to circumvent theintractability of the polymer. For example, a variety of co-monomershave been introduced in the PTFE macromolecular chains that lead toco-polymers of reduced viscosity and melting temperature. Co-polymersare those that are polymerized with, for example, hexafluoropropylene,perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether),perfluoro(propyl vinyl ether), or perfluoro-(2,2-dimethyl-1,3-dioxole),partially-fluorinated monomers and combinations thereof, in addition tothe tetrafluoroethylene monomer. Several of the resulting co-polymers(for example, those referred to as FEP, MFA, PFA and Teflon® AF) provideimproved processibility, and can be processed with techniques for commonthermoplastic polymers (WO 98/58105). However, a penalty is paid interms of some or all of the outstanding properties of the homopolymerPTFE, such as reduced melting temperature and thermal and chemicalstability.

Additional methods to process the PTFE homopolymer include, for example,the addition of lubricants, plasticizers, and processing aids, as wellas oligomeric polyfluorinated substances and hydrocarbyl terminatedTFE-oligomers (for example, Vydax® 1000) (U.S. Pat. Nos. 4,360,488;4,385,026 and WO 94/02547). The latter method, however, is directed tothe improvement of the creep resistance of common PTFE which results ina bimodal morphology with two distinct melting temperatures, andgenerally does not lead to homogeneous PTFE compositions that can bemelt-processed according to standard methods. For example, only ahot-compression molding method is heretofore known for mixtures ofstandard PTFE and Vydax® 1000, that preferably is carried out in thenarrow temperature range between about 330° C. to 338° C. The otheraforementioned additions of lubricants, plasticizers, and processingaids also do not yield truly melt-processible PTFE compositions.Solution processing, at superautogeneous pressure, of PTFE fromperfluoroalkanes containing 2-20 carbon atoms has been disclosed in WO94/15998. The latter process is distinctly different frommelt-processing methods. Also disclosed is dispersion, and subsequentmelt-processing of standard PTFE into thermoplastic (host-) polymerssuch as polyetheretherketone and polyphenylene sulfide (WO 97/43102) andpolyacetal (DE 41 12 248 A1). The latter method compromises importantphysico-chemical properties of the resulting composition, when comparedto neat PTFE, or requires uneconomical and cumbersome removal of thehost material.

There exist PTFE grades of low molecular weight and of low viscosity.These grades, which are often are referred to as micropowders, commonlyare used as additives in inks, coatings and in thermoplastic and otherpolymers to impair, for example, nucleation, internal lubrication orother desirable properties that, in part, stem from the uniquephysico-chemical properties of the neat PTFE. Low molecular weight PTFEgrades, in their solid form, unfortunately, exhibit extreme brittlenessand, according to at least one of the suppliers, these PTFE grades . . .“are not to be used as molding or extrusion powders” (Du Pont, Zonyl®data sheets andurl:http://www.dupont.com/teflon/fluoroadditives/about.html—Jul. 7,1998).

Thus, a need continues to exist to develop melt-processible,thermoplastic poly(tetrafluoroethylene)s to exploit the outstandingproperties of this polymer in a wider spectrum of product forms, as wellas to enable more economical processing of this unique material.

SUMMARY OF THE INVENTION

Surprisingly, it has been found that poly(tetrafluoroethylene)s of aparticular set of physical characteristics provide a solution to theabove, unsatisfactory situation.

Accordingly, it is one objective of the present invention to providemelt-processible, thermoplastic PTFE compositions of good mechanicalproperties comprising PTFE grades that are characterized as having anon-zero melt-flow index in a particular range. As used hereinafter, theindication “good mechanical properties” means the polymer has propertiessuitable for use in thermoplastic applications, preferably includingapplications such as melt-processed thermoplastic formed intounoriented, solid fibers or films exhibiting an elongation at break ofat least 10%, determined under standard ambient conditions at a rate ofelongation of 100% per min.

Yet another object of the present invention is to providemelt-processible PTFE of good mechanical properties that exhibit aplateau value of the complex viscosity measured at frequencies belowabout 0.01 rad/s and at a temperature of 380° C. that is in a rangebeneficial for processing.

Another object of the present invention is to provide melt-processiblePTFE that in its unoriented solid form has a crystallinity of betweenabout 1% and about 60% and good mechanical properties.

Still another object of the present invention is to provide amelt-blending method that yields melt-processible, thermoplastic PTFEcompositions of good mechanical properties comprising PTFE grades thatare characterized in having a non-zero melt-flow index in a particularrange.

Additionally, it is an object of the present invention to provide amethod to melt-process PTFE compositions that comprise PTFE grades thatare characterized in having a non-zero melt-flow index in a particularrange, into useful shapes and articles of good mechanical properties.

Still another object of the present invention is to provide usefulshapes and articles of good mechanical properties that are manufacturedby melt-processing of PTFE compositions that comprise PTFE grades thatare characterized in having a non-zero melt-flow index in a particularrange.

Yet another object of this invention is to provide novel useful shapesand articles that comprise PTFE.

Additional objects, advantages and novel features of the presentinvention will be set forth in part in the description which follows,and in part will become apparent to those skilled in the art onexamination of the following, or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

The present invention provides a melt-processible fluoropolymer having apeak melting temperature of at least 320° C. and good mechanicalproperties. And compositions and articles comprising at least in part acontinuous polymeric phase comprising a melt-processible fluoropolymerhaving a peak melting temperature of at least 320° C. and goodmechanical properties.

The present invention also provides a composition comprising amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.And a process for producing a melt-processible composition comprising amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.Also a method for producing an article comprising melt-processing acomposition comprising a melt-processible tetrafluoroethylene polymer,or a melt-processible blend of two or more tetrafluoroethylene polymerswherein said polymer or said blend of two or more polymers has goodmechanical properties.

Another aspect of the present inventions includes using themelt-processible polymer or polymer composition as an adhesive. Thepresent invention provides a process for connecting parts comprisingadhering a part to at least one further part with the polymer orcomposition of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a stress-strain curve of a melt-processed film of PTFEaccording to the present invention.

FIG. 2 is a prior art commercial, sintered and skived film of standard(ultra-high molecular weight) PTFE.

DETAILED DESCRIPTION OF THE INVENTION

The following is a list of defined terms used herein:

Void free—refers to a polymer or polymer composition below itscrystallization temperature, having a void content lower than sinteredtetrafluoroethylene polymers including sintered tetrafluoroethylenepolymers modified up to 0.1 wt % with PPVE (which are reported to have avoid content of 2.6% or higher in the Modern Fluoropolymers, J. Scheirs,Ed. Wiley (New York 1997) at p. 253). Preferably, void free refers to apolymer or polymer composition, below its crystallization temperature,having a void content lower than 2% as determined by measuringgravimetrically the (apparent) density of a specimen and the intrinsicdensity via its IR spectroscopically determined amorphous content (asdiscussed in the Modern Fluoropolymers, J. Scheirs, Ed. Wiley (New York1997) at pp. 240-255, in particular p. 253; the entire disclosure ofwhich is, 1997, p. 240).

Monomeric units—refers to a portion of a polymer that corresponds to themonomer reactant used to form the polymer. For example, —CF₂CF₂—represents a monomeric unit derived from the monomer reactanttetrafluoroethylene.

The poly(tetrafluoroethylene)s

The PTFE's according to the present invention generally are polymers oftetrafluoroethylene. Within the scope of the present invention it iscontemplated, however, that the PTFE may also comprise minor amounts ofone or more co-monomers such as hexafluoropropylene, perfluoro(methylvinyl ether), perfluoro(propyl vinyl ether),perfluoro-(2,2-dimethyl-1,3-dioxole), and the like, provided, howeverthat the latter do not significantly adversely affect the uniqueproperties, such as thermal and chemical stability of the PTFEhomopolymer. Preferably, the amount of co-monomer does not exceed about5 weight percent, and more preferred are PTFE's that comprise less thanabout 1 weight percent of co-monomer. Preferably, the amount of suchco-monomer does not exceed about 3 mole percent (herein “mol %’), andmore preferably less than about 1 mol %, particularly preferred is aco-monomer content of less than 0.5 mol %. In the case that the overallco-monomer content is greater than 0.5 mol %, it is preferred thatamount of the a perfluoro(alkyl vinylether) co-monomer is less thanabout 0.5 mol %; and more preferably less than about 0.2 mol %. Suitablepolymers include those having a peak melting temperature, as measuredunder standard conditions, that exceeds about 320° C., preferably above325° C. and more particularly above 327° C. Preferably the polymer willhave no peak melting temperatures below 320° C. and more preferably thepolymer will have a single peak melting point which is above 320° C.Most preferred are PTFE homopolymers.

In addition, suitable poly(tetrafluoroethylene)s according to thepresent invention include those having good mechanical properties, suchas, for example, a highly beneficial thermoplastic flow behavior. Anindication of the thermoplastic flow behavior of the polymer can bereadily analyzed with the commonly employed method of the determinationof a melt-flow index (MFI). The latter method, for the present PTFE's isconveniently and reproducibly carried out according to ASTM testD1238-88, at 380° C. under a load of 21.6 kg, herein referred to as themelt flow index or alternatively MFI (380/21.6). Under theseexperimental conditions, and in a maximum extrudate-collection time of 1hr, conventional ultra-high molecular weight PTFE grades have an MFI ofzero. Preferably, the PTFE grades according to the present inventionhave a non-zero MFI (380/21.6) of less than about 50 g/10 min in amaximum extrudate-collection time of 1 hr. More preferably, the PTFE'sare characterized by an MFI (380/21.6) between about 0.0005 and about25g/10 min. Although the choice of the PTFE grades used will to someextent depend on the particular end product, an MFI range of about 0.25to about 2 g/10 min is preferred for most applications.

Preferably, the PTFE grades according to the present invention have anon-zero MFI (380/21.6) of less than about 2.5 g/10 min in a maximumextrudate-collection time of 1 hr. More preferably, the PTFE's arecharacterized by an MFI (380/21.6) between about 0.0005 and about 2.5g/10 min, more preferably between about 0.2 g/10 min and about 2.5 g/10min and most preferably between 0.25 g/10 min and about 2.5 g/10 min.Although the choice of the PTFE grades used will to some extent dependon the particular end product, an MFI range of about 0.25 to about 2g/10 min is preferred for most applications. In the case that the PTFEgrades according to the present invention comprise a relatively highcontent of comonomer the upper limit of the MFI range of the preferredgrades could be higher. For example, if the PTFE contains up to 3 mol %of comonomer, the upper limit of the MFI range could extend up to about25 g/10 min, and a preferred range would be between 0.1 up to about 15;when the comonomer content is about 1 mol % or less, the MFI range mayextend up to about 15 g/10 min, more preferably the MFI range would bebetween 0.1 up to about 10; and at a content of 0.3 mol % or less thesuitable MFI would next exceed about 5 g/10 min and more preferablywould have an MFI value in the above-noted range for PTFE polymers.

The highly beneficial thermoplastic flow behavior of thepoly(tetrafluoroethylene)s according to the present invention ischaracterized by their linear visco-elastic behavior, which isconveniently expressed as the absolute value of the complex viscosity.Preferably, the PTFE grades according to the present invention have aplateau value of the complex viscosity measured at frequencies belowabout 0.01 rad/s and at a temperature of 380° C. of between about 4.10⁵and about 10⁹ Pa.s; preferably between about 7.10⁵ and about 10⁸ morepreferably at least 1.5×10⁷ Pa.s; and most preferred between about 10⁶and about 5.10⁷ Pa.s.

The poly(tetrafluoroethylene)s according to the present invention inaddition to having good mechanical properties, are characterized in arelatively low crystallinity which is beneficial for the toughness ofproducts fabricated thereof. This degree of crystallinity isconveniently determined by differential scanning calorimetry (DSC)according to standard methods known to those skilled in the art ofpolymer analysis. Preferably, once-molten PTFE grades according to thepresent invention that are recrystallized by cooling under ambientpressure at a cooling rate of 10° C./min in unoriented form have adegree of crystallinity of between about 1% about 60%, preferablybetween about 5% and about 60%, more preferably at least about 45% andnot more than 55% based on a value of 102.1 J/g for 100% crystallinePTFE (Starkweather, H. W., Jr. et al., J. Polym. Sci., Polym. Phys. Ed.,Vol. 20, 751 (1982)).

Preferably, the PTFE grades according to the present invention arecharacterized by an MFI (380/21.6) between about 0.25 to about 2 g/10min and a degree of crystallinity of once-molten and recrystallizedunoriented material of between about 5%, preferably above 45% and lessthen about 60%, preferably less than 55%. More preferably, the PTFEpolymer is a polymer having a single peak melting point temperaturewhich is above 325° C. and is preferably a homogenous blend of polymersand/or homopolymer.

The PTFE grades of the present invention can be synthesized according tostandard chemical methods for the polymerization of tetrafluoroethyleneas described in detail in the literature (for example, W. H. Tuminelloet al., Macromolecules, Vol. 21, pp. 2606-2610 (1988)) and as practicedin the art. Additionally, PTFE grades according to the present inventioncan be prepared by controlled degradation of common, high molecularweight PTFE, for example by controlled thermal decomposition, electronbeam, gamma- or other radiation, and the like (Modern Fluoropolymers, J.Scheirs, Ed. Wiley (New York), 1997 the entire disclosure of which ishereby incorporated by reference). Furthermore, and as demonstrated inthe present invention, the PTFE grades according to the presentinvention can be manufactured by blending of, for example, highmelt-flow index grades with appropriate amounts of grades of a lower,for instance below 0.5 g/10 min, or even zero melt-flow index to yieldmixed materials with values of the melt-flow index, viscosity orcrystallinity in the desired range. Due to the relatively simple natureof the MFI-testing method, viscosity measurement and crystallinitydetermination, using, for example, these analytical tools, those skilledin the art of polymer blending can readily adjust the relative portionsof the different PTFE grades to obtain the melt-processible,thermoplastic PTFE compositions according to the present invention.

The present invention also contemplates compositions and articlescomprising a continuous phase having at least 15 wt. %, preferably atleast 45 wt. %, and more preferably at least 95 wt. % of themelt-processible tetrafluoroethylene polymer including polymers that areformed by blending two or more tetrafluoroethylene polymers of thepresent invention. An exemplary composition could include a compositionor an article wherein the continuous phase composed of at least 99 wt. %of a PTFE homopolymer filled with a filler such as talc, glass and/orother inorganic or organic particles. It may be that the filler comprisea between 10 to 90 wt. %, preferably between 10 and 45 wt % and morepreferably less than 30 wt. % of the total composition (includingcontinuous phase and filler).

The compositions according to the present invention optionally mayinclude other polymers, additives, agents, colorants, fillers (e.g.,reinforcement and/or for cost-reduction), property-enhancement purposesand the like, reinforcing matter, such as glass-, aramid-, carbon fibersand the like, plasticizers, lubricants, processing aids, blowing orfoaming agents, electrically conducting matter, other polymers,including poly(tetrafluoroethylene), fluorinated polymers andcopolymers, polyolefin polymers and copolymers, and rubbes andthermoplastic rubber blends, and the like. Depending on the particularapplication, one or more of the above optional additional ingredientsand their respective amounts are selected according to standardpractices known to those skilled in the art of standard polymerprocessing, compounding and applications.

Processing

The PTFE compositions according to the present invention can beprocessed into useful materials, neat or compounded, single- andmulti-component shapes and articles using common melt-processing methodsused for thermoplastic polymers that are well known in the art. Typicalexamples of such methods are granulation, pelletizing, (melt-)compounding, melt-blending, injection molding, melt-blowing,melt-compression molding, melt-extrusion, melt-casting, melt-spinning,blow molding, melt-coating, melt-adhesion, welding, melt-rotationmolding, dip-blow-molding, melt-impregnation, extrusion blow-molding,melt-roll coating, embossing, vacuum forming, melt-coextrusion, foaming,calendering, rolling, and the like.

Melt-processing of the PTFE compositions according to the presentinvention, in its most general form, comprises heating the compositionto above the crystalline melting temperature of the PTFE's, which, ofonce-molten material, typically are in the range from about 310 to about335° C., e.g. from about 320° C. to about 335° C. (preferably less than400° C.), although somewhat lower, and higher temperatures may occur, toyield a viscous polymer fluid phase. Unlike standard (ultra-highmolecular weight) PTFE above its crystalline melting temperature, thePTFE grades according to the present invention form homogenous meltsthat can be freed from voids and memory of the initial polymer particlemorphology. The latter melt is shaped through common means into thedesired form, and, subsequently or simultaneously, cooled to atemperature below the crystalline melting temperature of the PTFE's,yielding an object or article of good and useful mechanical properties.In one preferred embodiment, shaped PTFE melts are rapidly quenched at acooling rate of more than 10° C./min, more preferably more than 50°C./min, to below the crystallization temperature to yield objects, suchas fibers and films, of higher toughness.

Certain articles, such as, but not limited to, fibers and films madeaccording to the present invention optionally may, subsequently, bedrawn or otherwise deformed in one or more directions, embossed, and thelike to further improve the physico-chemical, mechanical, barrier,optical and/or surface properties, or be otherwise post-treated (forinstance, quenched, heat treated, pressure treated, and/or chemicallytreated). The above methods and numerous modifications thereof and otherforming and shaping, and post-processing techniques are well know andcommonly practiced. Those skilled in the art of processing ofthermoplastic polymers are capable of selecting the appropriatemelt-processing and optional post-processing technology that is mosteconomical and appropriate for the desired end product, or productintermediate.

Products and Applications

The products contemplated according to the present invention arenumerous, and cover vastly different fields of applications. This isespecially true as PTFE has been approved for food contact and forbiomedical applications. Without limiting the scope and use of thepresent invention, some illustrative products are indicated hereafter.Generally speaking, the products and materials according to the presentinvention include most or all applications that currently are covered bystandard (ultra-high molecular weight) PTFE, and many of its modified,melt-processible co-polymers. In many cases, the present products, whencompared with the latter, will have superior physical-chemicalproperties due to their predominant homopolymer character. Thus,applications are envisioned, among other industries, in the wire andcable industry, the printed-circuit board industry, the chemicalprocessing industry, the semiconductor industry, the automotiveindustry, out-door products and coatings industry, the food industry,the biomedical industry, and more generally in industries and uses whereany combination of high release, anti-stick, high-temperature stability,high chemical resistance, flame-resistance, anti-fouling, UV resistance,low friction, and low dielectric constant is required.

In particular, the PTFE may be used to form at least parts in articlessuch as, for example, is a wire (and/or wire coating), an optical fiber(and/or coating), a cable, a printed-circuit board, a semiconductor, anautomotive part, an outdoor product, a food, a biomedical intermediateor product, a composite material, a melt-spun mono- or multi-filamentfiber, an oriented or un-oriented fiber, a hollow, porous or densecomponent; a woven or non-woven fabric, a filter, a membrane, a film, amulti-layer- and/or multicomponent film, a barrier film, a container, abag, a bottle, a rod, a liner, a vessel, a pipe, a pump, a valve, anO-ring, an expansion joint, a gasket, a heat exchanger, aninjection-molded article, a see-through article, a sealable packaging, aprofile, and/or a thermoplastically welded part. Preferred articles mayinclude fibers, films, coatings and articles comprising the same.

Typical examples of intermediate and end-user products that can be madeaccording to the present invention include, but are not limited togranulate, thermoplastic composites, melt-spun mono- and multi-filamentfibers, oriented and not, hollow, porous and dense, single- andmulti-component; fabrics, non-wovens, cloths, felts, filters, gas housefiltration bags; sheets, membranes, films (thin and thick, dense andporous); containers, bags, bottles, generally simple and complex parts,rods, tubes, profiles, linings and internal components for vessels,tanks, columns, pipes, fittings, pumps and valves; O-rings, seals,gaskets, heat exchangers, hoses, expansion joints, shrinkable tubes;coatings, such as protective coatings, electrostatic coatings, cable andwire coatings, optical fiber coatings, and the like. The above productsand articles may be comprised in part or in total PTFE compositionsaccording to the present invention, or optionally include dissimilarmaterials, such as for example in multi-layer and multi-component films,coatings, injection molded articles, containers, pipes, profiles, andthe like.

Due to the fact that the PTFE grades according to the present inventioncan be readily processed into mechanical coherent, tough, thin, denseand/or translucent objects, novel application areas for PTFE arecontemplated that heretofore were not readily or economically, if atall, accessible due to the intractability of standard (ultra-highmolecular weight) grades, notably in areas where the absence of remnantsof powder morphology and voids have prohibited use of the lattermaterial. Preferably, the polymer of the present invention hassufficient clarity such that if it were formed into a 1 mm thick film,and tested at a temperature below its crystallization temperature, itwould be sufficiently translucent to enable images viewed through thefilm to be readily recognized, preferably without distortion.

Exemplary applications of the polymer and polymer composition of thepresent which take advantage of some of these beneficial propertiesinclude see-through, sealable packaging, barrier films and caps,conformal coatings, dense tubing and linings, thin-walled and complexinjection-molded parts, and the like.

The PTFE grades according to the present invention, due to theirthermoplastic nature, not only are useful for the simple and economicproduction of finished goods and intermediate products, but also forother functions. An illustrative example of such function, withoutlimiting the scope of the present invention, is adhesion and welding.The latter is a well-recognized difficulty associated with common PITE(Modern Fluoropolymers, J. Scheirs, Ed. Wiley (New York), 1997, p. 251).The PTFE grades according to the present invention were found to beoutstanding adhesives, for example, for itself as well as for otherfluoropolymers, preferably including common high-molecular weight PTFEproducts such as films, sheets and the like. Simply by inserting a smallamount of a PTFE grade according to the present invention in powder,film or other form between two or more surfaces that one desires toadhere together, liquefying the former material, and subsequentlysolidifying under slight or modest pressure, it was found to yield avery strong adhesive bond that was provided by the inventive PTFEgrades.

The following specific examples are presented to illustrate variousaspects of the present invention and are not to be construed aslimitations thereon.

EXAMPLE

The following examples are given as particular embodiments of theinvention and to demonstrate the practice and advantages thereof. It isunderstood that the examples are given by way of illustration and arenot intended to limit the specification or the claims that follow in anymanner.

General Methods and Materials

Melt-Flow Index. Values of the melt flow index (MFI) as discussed hereinare determined in accordance with the ASTM Standard D1238-88 at atemperature of 380° C. and under a load of 21.6 kg during a maximumextrudate-collection time of 1 hr using a Zwick 4106 instrument.

Viscosity. The absolute values of the complex viscosities of differentPTFE grades were measured from small amplitude oscillatory shearexperiments (Rheometrics Dynamic Spectrometer RDS-II) at 380° C. forseveral frequencies between 100 rad/s and 3.10⁻³ rad/s using standardplate-plate geometry. The linear range was estimated from strain-sweepexperiments at 100 rad/s.

Thermal Analysis. Thermal analysis was conducted with a Netzschdifferential scanning calorimeter (DSC, model 200). Samples of about 5mg were heated at a standard rate of 10° C./min. Melting temperaturesgiven hereafter refer to the endotherm peak temperatures of once molten(at 380° C.) and cooled (at 10° C./min) material. Crystallinities weredetermined from the enthalpies of fusion of the same specimen taking thevalue of 102.1 J/g for 100% crystalline PTFE (Starkweather, H. W., Jr.et al., J. Polym. Sci., Polym. Phys. Ed., Vol. 20, 751 (1982)).

Mechanical Data. Tensile tests were carried out with an Instron TensileTester (model 4411) at room temperature on dumbbell-shaped specimen of12 mm gauge length and 2 mm width and fibers. The gauge fiber length was20 mm. The standard rate of elongation was 100%/min.

Materials. Various grades of PTFE, purchased from Du Pont (Teflon®,Zonyl®), Ausimont (Algoflon®) and Dyneon, were used. The following TableI presents an overview of the melting temperatures and thecrystallinities of materials that were once molten at 380° C. andrecrystallized by cooling at 10° C./min, and MFI (380/21.6) of thedifferent grades, which include grades both outside the invention, andthose according to the present invention.

TABLE I Melting Crystal- MFI PTFE Temperature* linity (380/21.6) grade(° C.) (%) (g/10 min) I Zonyl ® 1200 325.9 64.8 >>1,000 II Zonyl ® 1100325.0 67.2 >1,000 III Zonyl ® 1600 329.0 68.9 150 IV Dyneon ® 9207 329.865.1 55 V Zonyl ® 1000 329.3 59.5 52 VI blend V/XX** 331.6 60.5 35 VIIDyneon ® 9201 330.5 60.9 22 VIII blend V/XX** 331.4 59.9 15 IX Zonyl ®1300 329.9 60.5 10 X Algoflon ® F5A EX 330.7 61.7 9 XI Zonyl ® 1400330.8 57.3 2.8 XII Algoflon ® L206 332.3 60.8 2.6 XIII blend IX/XX**331.2 51.9 1.8 XIV blend XI/XIX** 329.3 49.9 1.2 XV blend V/XIX** 329.451.4 1.0 XVI blend XI/XIX** 329.7 47.6 0.8 XVII blend IX/XX** 330.5 50.90.8 XVIII blend IX/XX** 331.5 47.5 0.6 XIX Zonyl ® 1500 327.5 44.2 0.2XX Teflon ® 6 328.6 33.7 0 *Note: all grades exhibited the well-knowthermal transitions around room temperature. typical of PTFE, and onlyone main melting endotherm at the elevated temperatures above indicated.**for compositions and preparation of blends see Example 7.

Comparative Example A

PTFE grades I-XII (Table I) were melt-compression molded at 380° C. witha Carver press (model M, 25 T) for 5 min at 1 metric ton (t), 10 min at10 t, and then cooled to room temperature during 4 min under 4 t intoplaques of about 4×4×0.1 cm. All grades were found to yield brittleproducts most of which could not be removed from the mold withoutfracture. This example shows that neat grades of PTFE of MFI values morethan about 2.5 cannot be employed to melt-process articles of usefulmechanical properties.

Example 1

Example A was repeated with PTFE grades XIII-XVIII. The materials weremelt-compression molded at 380° C. with a Carver press (model M, 25 T)for 5 min at 1 metric ton (t), 10 min at 10 t, and then cooled to roomtemperature during 4 min under 4 t into plaques of about 4×4×0.1 cm.These grades were found to yield mechanically coherent, and translucentsamples that could readily be removed from the mold and bend withoutfracture. This example shows that grades of a non-zero MFI value, butless then about 2.5 can be employed to melt-process articles of PTFE ofuseful mechanical properties.

Comparative Example B

Attempts were made to melt-compression mold at 380° C. with a Carverpress (model M, 25 T) films of PTFE grades I-XII. All grades were foundto yield brittle products that could not be mechanically removed fromthe mold without fracture. This example shows that neat grades of MFIvalues more then about 2.5 cannot be employed to produce melt-processed,free-standing films of useful mechanical properties.

Example 2

Example B was repeated with PTFE grades XIII-XVIII. The materials weremelt-compression molded at 380° C. with a Carver press (model M, 25 T)for 5 min at 1 metric ton (t), 10 min at 10 t, and then cooled to roomtemperature during 4 min under 4 t into thin films of about 15×1533about 0.025 cm. These grades were found to yield mechanically coherent,translucent and flexible films that could readily be removed from themold. This example shows that grades of a non-zero MFI value, but lessthen about 2.5 can be employed to melt-process thin, mechanicallycoherent films of PTFE.

The mechanical properties of the melt-processed PTFE films were measuredaccording to the standard method detailed above. A typical stress-straincurve is presented in FIG. 1 (A), for comparison purposes, together withthat of a sample of commercial, pre-formed/sintered and skived film of0.40 mm thickness (B). This figure shows that the melt-processed PTFEfilm (here of grade XVI (Table I)) has the typical deformationproperties of a thermoplastic, semi-crystalline polymer with a distinctyield point and strain hardening. The stress-strain curves A and Bresemble each other, which indicates that these melt-processed PTFEfilms do not have substantially inferior mechanical properties whencompared to common, PTFE of ultra-high molecular weight. The mechanicaldata of the two products are collected in Table II.

TABLE II Elongation Yield Stress Tensile Strength at Break PTFE film(MPa) (Nominal, MPa) (%) Skived Film 12.8 36.1 476 Melt-processed Filmof 12.6 20.9 427 PTFE grade XVI

The excellent mechanical properties of the film according to the presentinvention were not affected by storing the sample for periods in excessof 15 hrs at temperatures of 200° C. and higher.

In addition, we observed that the melt-processed PTFE films, unlike thecommercial skived material, were dense and translucent, through whichtext readily could be read up to a film thickness of about 1 mm.

Comparative Example C

PTFE grades I-XII and XX were introduced into a laboratory melt-spinningapparatus (SpinLine, DACA Instruments), the temperature of which waskept at 380° C., and that was equipped with a die of 1 mm diameter(length/diameter ratio 1). PTFE grades I-XII could not be collected asmonofilaments due to brittleness of the extrudate, leading to prematurefracture. Ultra-high molecular weight PTFE grade XX could not bemelt-spun, even at loads up to 5 kN (limit of equipment), due to thehigh viscosity (zero MFI) of the material.

Example 3

Example C was repeated with PTFE grade XV. PTFE monofilaments werecollected onto bobbins. The filaments were tough, and could readily bedrawn at room temperature to draw ratios exceeding 4.

The mechanical properties of the melt-spun fibers were measuredaccording to the method detailed above. Their tensile strength exceeded0.1 GPa.

Comparative Example D

PTFE grades I-XII and XX were introduced into a laboratory, recyclingtwin-screw extruder (MicroCompounder, DACA Instruments), the temperatureof which was kept at 380° C., and that was equipped with an exit die of2 mm diameter. PTFE grades I-XII could not be collected as continuousextrudates due to extreme brittleness of the extrudate, leading topremature fracture. Ultra-high molecular weight PTFE grade XX could notbe extruded due to the high viscosity (zero MFI) of the material.

Example 4

Example D was repeated with PTFE grades XIII-XVIII. Continuous PTFEextrudates were readily collected. The extrudates could readily bechopped into granulate or drawn into monofilaments.

Example 5

PTFE grade XV was melt-compounded at 380° C. in a Brabender DSK25segmented, co-rotating extruder (25 mm diameter; 22 aspect ratio) with0.1 weight % of various dyes (Amaplast® Blue HB, Red RP, Yellow NX,ColorChem Int. Corp.), 10% of TiO₂ (Fluka), 10 weight % of aramid pulp(Twaron®, Akzo Nobel), and 20 weight % of chopped, 15 mm long carbonfiber, respectively. Subsequently, the compounded materials obtainedwere melt-processed into plaques according to the method in Example 1.Optical microscopy on thin sections (about 0.1 mm) revealed that in allcases extremely homogeneous mixtures and composites were obtained. Thisexample shows that PTFE according to the present invention can bemelt-compounded.

Comparative Example E

Two strips of about 7×1×0.04 cm of commercial, skived film of highmolecular weight PTFE were pressed together in a Carver press (model M,25T) at a temperature of 380° C. under a load of less than 1 t for 2 minand subsequently cooled to room temperature. Without much force, thestrips could be separated from each other, which is indicative of pooradhesion, and illustrates the difficulties encountered in welding ofcommon PTFE.

Example 6

Example E was repeated. However, a small piece of melt-processed film ofPTFE grade XV (about 1×1×0.02 cm) was placed in between the two stripsof about 7×1×0.04 cm of commercial, skived film of high molecular weightPTFE. This sandwich structure was also pressed together in a Carverpress (model M, 25T) at a temperature of 380° C. under a load of lessthan 1 t for 2 min and, subsequently, cooled to room temperature. Thestrips could be separated from each other only after one or both of theskived material strips exhibited excessive plastic deformation, which isindicative of outstanding adhesive properties of this grade to, forexample, common PTFE.

Example 7

Various amounts (total quantity 90 g) of PTFE grades V and XIX, XI andXIX, and IX and XX, respectively, (see Table 1) were introduced into aBrabender melt-kneader (model Plasti-corder PL 2000), which was kept ata temperature of about 380° C., 60 rpm. After about 1 min, a clearhomogeneous melt was formed that behaved like a melt of ordinarythermoplastics. Mixing was continued for 10 min, after which the blendedproduct was discharged. The MFI values of the different blends weremeasured. The results are given in Table III.

TABLE III Weight Ratio MFI (380/21.6) PTFE grades (-) (g/10 min) IX + XX45-55 0.6 IX + XX 50-50 0.8 XI + XIX 10-90 0.8 V + XIX 12.5-87.5 1.0XI + XIX 25-75 1.2 IX + XX 60-40 1.8

This example shows that PTFE grades according to the present inventionof an MFI value in the desired range can be prepared by melt-blending ofPTFE grades of which one or more are of too high or/and too low valuesof their respective MFI.

Example 8

Various amounts (total quantity 90 g) of PTFE grades V and XIX, and IXand XX, respectively, (see Table 1) were introduced into a Brabendermelt-kneader (model Plasti-corder PL 2000), which was kept at atemperature of about 380° C., 60 rpm. After about 1 min, a clearhomogeneous melt was formed that behaved like a melt of ordinarythermoplastics. Mixing was continued for 10 min, after which the blendedproduct was discharged. The absolute values of the complex viscositiesof various PTFE samples were measured from small amplitude oscillatoryshear experiments. The results are given in Table IV.

TABLE IV Weight Ratio Viscosity PTFE grades (-) (Pa.s) V + XIX 60-409.3. 10⁵ V + XIX 40-60 5.5. 10⁶ V + XIX 20-80 8.4. 10⁶ V + XIX 10-901.3. 10⁷ IX + XX 60-40 1.2. 10⁷ IX + XX 50-50 1.8. 10⁷ IX + XX 45-552.4. 10⁷

The same PTFE samples were processed into films according to the methodin Example 2. All films were found to exhibit good mechanicalproperties.

Having described specific embodiments of the present invention, it willbe understood that many modifications thereof will readily appear or maybe suggested to those skilled in the art, and it is intended thereforethat this invention is limited only by the spirit and scope of thefollowing claims.

What is claimed is:
 1. A method for producing an article comprising:melt-processing a composition comprising a poly(tetrafluoroethylene)polymer, wherein said polymer has (i) a melt flow index between 0.25 andabout 50 g/10 min; (ii) an elongation to break of at least 10%; (iii) acrystallinity of 1-55%; (iv) less than 1 weight percent of co-monomer;and (v) less than 0.5 mol % of co-monomer; wherein all said co-monomerconsists essentially of co-monomer selected from the group consisting ofhexafluoropropylene and perfluoro(alkyl vinylether).
 2. The method ofclaim 1, wherein said melt-processing includes injection molding.
 3. Themethod of claim 1, wherein said melt-processing includes melt-extruding.4. The method of claim 1, wherein said melt-processing includesmelt-spinning.
 5. The method of claim 1, wherein said polymer has acrystalline melting temperature in the range of about 310 to about 335°C.
 6. The method of claim 1, wherein said polymer has no peak meltingtemperature below 320° C.
 7. The method of claim 1, wherein saidcomposition further comprises a filler.
 8. The method of claim 1,wherein said polymer comprises a perfluoro(alkyl vinylether) co-monomer.9. The method of claim 1, wherein said polymer comprisesperfluoro(propyl vinyl ether) co-monomer.
 10. The method of claim 1,wherein said melt flow index is at least 1.0 g/10 min.
 11. The method ofclaim 1, wherein said composition comprises a furtherpoly(tetrafluoroethylene) polymer.
 12. The method of claim 11, whereinsaid further poly(tetrafluoroethylene) polymer has a melt flow indexbelow 0.5 g/10 min.
 13. The method of claim 1, wherein said compositioncomprises at least 45 wt % of said polymer.
 14. The method of claim 1,wherein said composition comprises at least 95 wt % of said polymer. 15.The method of claim 1, wherein said polymer has a void content below 2%.16. The method of claim 1, wherein said composition consists essentiallyof: (i) said polymer; and (ii) at least one ingredient selected from thegroup consisting of reinforcing matter, electrically conducting matter,blowing agents, foaming agents, fillers, and colorants.
 17. An articleobtained by the method of claim
 1. 18. The method of claim 1, whereinsaid polymer has a draw ratio exceeding
 4. 19. The method of claim 1,wherein said method includes heating said composition to a temperatureabove the crystalline melting temperature of said polymer.
 20. Themethod of claim 10, wherein said polymer has a draw ratio exceeding 4.21. The method of claim 10, wherein said method includes heating saidcomposition to a above the crystalline melting temperature of saidpolymer.
 22. A method for producing an article comprising:melt-processing a composition comprising a poly(tetrafluoroethylene)polymer, wherein said poly(tetrafluoroethylene) polymer has (i) anon-zero melt flow index; (ii) an elongation to break of at least 10%;(iii) a crystallinity of 1-55%; (iv) a crystalline melting temperaturein the range of about 310 to about 335° C.; and wherein saidpoly(tetrafluoroethylene) polymer comprises co-monomer, said co-monomerconsisting essentially of perfluoro(alkyl vinylether) co-monomer, andsaid co-monomer being present in an amount of less than 1 weight percentand less than 0.5 mol %.
 23. The method of claim 22, wherein saidmelt-processing includes injection molding.
 24. The method of claim 22,wherein said melt-processing includes melt-extruding.
 25. The method ofclaim 22, wherein said melt-processing includes melt-spinning.
 26. Themethod of claim 22, wherein said composition further comprises a filler.27. The method of claim 22, wherein said co-monomer is aperfluoro(propyl vinyl ether) co-monomer.
 28. The method of claim 22,wherein said polymer has no peak melting temperature below 320° C. 29.The method of claim 22, wherein said melt flow index is at most about 50g/10 min.
 30. The method of claim 22, wherein said melt flow index is atleast 1.0 g/10 min.
 31. The method of claim 22, wherein said compositioncomprises at least 45 wt % of said polymer.
 32. The method of claim 22,wherein said composition comprises at least 95 wt % of said polymer. 33.The method of claim 22, wherein said polymer has a void content below2%.
 34. The method of claim 22, wherein said composition consistsessentially of: (i) said polymer; and (ii) at least one ingredientselected from the group consisting of reinforcing matter, electricallyconducting matter, blowing agents, foaming agents, fillers, andcolorants.
 35. An article obtained by the method of claim
 22. 36. Amethod for producing an article comprising: melt-processing acomposition comprising a blend of two or more poly(tetrafluoroethylene)polymers, wherein said blend has (i) a non-zero melt flow index; (ii) amelting temperature in the range of 310° C. to about 335° C.; (iii) anelongation to break of at least 10%; and (iv) a crystallinity of 1-55%;and wherein at least two of said two or more poly(tetrafluoroethylene)polymers have a co-monomer content below 1 wt %.
 37. The method of claim36, wherein said melt-processing includes injection molding.
 38. Themethod of claim 36, wherein said melt-processing includesmelt-extruding.
 39. The method of claim 36, wherein said melt-processingincludes melt-spinning.
 40. The method of claim 36, wherein all of saidtwo or more poly(tetrafluoroethylene) polymers comprise less than 1 wt %co-monomer.
 41. The method of claim 36, wherein saidpoly(tetrafluoroethylene) polymer comprises perfluoro(propyl vinylether) co-monomer.
 42. The method of claim 36, wherein saidpoly(tetrafluoroethylene) polymer comprises hexafluoropropyleneco-monomer.
 43. The method of claim 36, wherein said melt flow index isat least 1.0 g/10 min.
 44. The method of claim 36, wherein saidcomposition further comprises a filler.
 45. The method of claim 36,wherein said composition consists essentially of said blend.
 46. Themethod of claim 36, wherein said composition consists essentially of (i)said blend; and (ii) at least one ingredient selected from the groupconsisting of reinforcing matter, electrically conducting matter,blowing agents, foaming agents, fillers, and colorants.
 47. An articleobtained by the method of claim
 36. 48. The method of claim 36, whereinsaid blend has a draw ratio exceeding
 4. 49. The method of claim 36,wherein said method includes heating said composition to a temperatureabove the crystalline melting temperature of said two or morepoly(tetrafluoroethylene) polymers.